DEACYLATION AND CLEAVAGE OF CELL WALLS OF PANGOLA GRASS WITH BOROHYDRIDE

Article abstract of DOI:10.1016/0031-9422(89)80019-6

Aqueous borohydride (pH 9) removed up to 97percent of acetyl groups from glucose pentaacetate, myo-ionositol hexaacetate and cellulose acetate in 48 hr.When cellulase-digested pangola grass stem cell walls, which were resistant to further degradation with dresh 'cellulase' (Onozuka P-1500), were stirred with borohydryde under the same conditions, 30percent of the cell walls were solubilized.The cell wall residue could now be further degraded (36percent) with 'cellulase'.The residue retained 45percent of the original esterified trans-p-coumaric acid and 20percent of the acetate.The borohydride soluble fraction, which contained ca half of the original p-coumaric acid still esterified, on neutralization gave a solution containing mainly hemicellulosic carbohydrates and negligible p-coumaric acid, and a precipitate consisting of lignin (75percent), esterified p-coumaric acid (5percent) and carbohydrate (20percent) comprising mainly pentoses.The neutral soluble material was fractionated by gel filtration to yield polymeric and oligomeric carbohydrate.Substances retarded on the column consisted of aromatic residues spectroscopically similar to lignin and contained a small amount of bound carbohydrate, of which the major components were glycerol, arabinose, xylose, glucose and xylitol.The results indicated that part of the cell walls were bound together by many borohydride-labile linkages, probably aliphatic esters.The variety of structures isolated from the borohydride soluble material, some still containing aromatic and carbohydrate residues bound together, suggests that borohydride may be a useful reagent in studies aimed at elucidation of in situ cell wall structures which limit biodegradability.Key Word Index - Digitaria decumbens; Gramineae; tropical grass; cell walls; borohydride; deacylation; acetate; p-coumaric acid; lignin; hemicellulose; gel filtration.